The following information is provided to assist the reader in understanding technologies disclosed below and the environment in which such technologies may typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the technologies or the background thereof. The disclosure of all references cited herein are incorporated by reference.
Chlorination of water supplies is the most prevalent form of water disinfection. Chlorination introduces oxidizing agents that kill microorganisms present in the water. The two primary water disinfectants used in the United States are free chlorine (as hypochlorite) and chloramines (compounds of chlorine and ammonia).
Measurement of chlorine levels in water is used to determine the amount of chlorination needed for a water supply. Accurate determination of chlorine levels in water is very important to ensure safety. Overestimation of chlorine levels can lead to dangerously inadequate disinfection, while underestimation of chlorine levels and associated over-chlorination can lead to unwanted by products, as well as unpleasant tastes and odors.
There are several analytical methods for the determination of chlorine in water. The most widely used analytical method is the DPD (N, N-diethyl-p-phenylenediamine) method. Absorbance (for example, at 515 nm) may, for example, be spectrophotometrically measured to determine free chlorine, chloramines, and/or total chlorine concentration.
Analytical instruments for chlorine species analysis, such as spectrometers used in, for example, the DPD chlorine method, may be tested and/or calibrated using standards. A standard is a composition that contains a known concentration of a chemical, species or analyte of interest. Standards are used, for example, to determine precision and accuracy of a test method, to determine proper functioning of test equipment, and skills and techniques of analysts. Unfortunately, standards for measuring chlorine species (including free chlorine and/or total chlorine) are limited because of an instability/relatively quick decomposition.